In current wireless communication systems such as LTE (Long Term Evolution) and HSPA (High Speed Packet Access), multi-antenna systems are used to increase capacity, coverage, and link reliability.
Future generations of cellular networks are expected to provide high data rates, up to 10 Gbps, while at the same time being energy efficient. One promising but relatively unexplored way to achieve such high data rates and/or to lower the energy consumption in cellular networks is to deploy reconfigurable antenna systems. A reconfigurable antenna system is an antenna system whose radiation characteristics can be changed by the network after deployment and adapted to, e.g., current traffic needs. For example, the antenna system can be reconfigured to better serve a traffic hotspot by, e.g., increasing the antenna gain toward the hotspot location.
Furthermore, there may be first type of beams for sector coverage where control and system information are transmitted, e.g., BCH (broadcast channel) and CRS (cell-specific reference signal) in LTE. Since these signals need to reach all users in a cell, they have to be transmitted with a sufficiently wide beam that covers the desired area. The beam should also be sufficiently narrow in order not to transmit too much interference into neighboring sectors. Typically, a beam with 65° half-power beamwidth (HPBW) is used for 3-sector sites, since this provides a good balance between the two conflicting requirements mentioned previously.
A second type of beams then relates to beams for user-specific data transmission, e.g., PDSCH (physical downlink shared channel) in LTE. These beams should be narrow in order to maximize the gain to the intended user and also to minimize the interference transmitted to other users.
Passive reconfigurable antennas typically contain two or more columns of antenna elements to be able to electrically change the beamwidth (BW) and/or beam pointing direction (BPD) in azimuth. Two or more such reconfigurable antennas can be combined into an antenna array that can be used for user-specific beamforming, spatial multiplexing, and other multi-antenna techniques. The phase center of each reconfigurable antenna in such an array is typically static and located in the middle of the reconfigurable antenna aperture. However, when using reconfigurable antennas to change the sector width in combination with codebook based precoding it is important to also adjust the phase center separation so that the codebook beams are matched to the new sector width.
With a traditional base station antenna, sector coverage is typically provided by a column of radiating elements connected via a feed network to a physical antenna port. The azimuth radiating pattern of the sector-covering beam is in this case given by the individual radiating element. Several such columns can then be assembled adjacent to each other to form an antenna array in the horizontal dimension. By applying beamforming weights to this array, user-specific beams can be created. In LTE, several transmission modes have been specified that make use of user-specific beamforming. One example is transmission mode 4 (TM4) where beamforming weights are selected from a set of predefined weights in a codebook, so called codebook-based precoding.
The flexibility in the sector beam generation can be utilized for sector shape reconfiguration when changes occur in the network such as changes in deployment or spatial traffic distribution, e.g., new sites, buildings, or traffic hotspots. It is well known that such reconfiguration can give substantial improvements in system performance.
It is therefore a desire to provide a node in a wireless communication system that comprises an antenna arrangement that enables changing of the sector width in wireless cellular networks, where all beams are matched to the new sector width.